Recently we assisted to the roll out first flight of the test aircraft for the Mitsubishi Regional Jet (MRJ) programme. The empennage of the MRJ is produced by a RTM process using dry fabrics .
We have found many informations published on the issue and we want to share with you some of the most interesting aspects we have read refering to the use of dry fabrics to manufacture the composite part in this project.
The company is developing a highly competitve aircraft. On the one hand, they are offering interesting operating costs with a good efficiency, in a big measure, thanks to light weight materials. On the other hand, they are working on a price competitive airplane, through improved production costs.
Cost reduction strategies:
- Precision on parts production for easing assembly.
- Lean manufacturing concepts like moving assembly lines: the product moves through the factory from one manufacturing process to the next.
- Circular body cross section for simplified tool design.
- Oven cured composite parts.
The composite empennage (horizontal and vertical stabilizers and fuselage interface) has been fabricated using an improved Liquid Moulding process called A-VaRTM. This process was developed jointly with Toray.
A-VaRTM molding technology is an advanced version of VaRTM. Vacuum Asisted Resin Transfer Moulding is a low cost composite manufacturing technique where, differing from prepreg laminated composites, the resin is infused into dry fabric, formed on a mold near product shape under vacuum pressure and cured in an oven.
A-VaRTM is a new version of it, suitable for aeronautic parts and with very good mechanical properties, by means of:
- Adoption of a fiber-reinforced base material with high quality and strength (dry Non Crimp Woven). Carbor fiber bundles form the primary structural element. Very fine glass fibers are used as auxiliary warp fiber to facilitate flow during resin infusion and to tie warp and auxiliary and fibers toghether.
- Application of thermoplastic particles designed to toughen the composite materials. They are used as a tackifier to consolidate the preform and also permit the use of a lower-viscosity and less expensive epoxy thermoset resin.
- Optimization of the forming process to obtain a high volume fraction of fiber (Vf = volume of fiber/volume of object × 100, targeted value 55 to 60%). MHI uses a proprietary diffusion or flow media to control the resin infusion flow and rate, as well as to bleed off excess resin. This maximizes fiber volume in the finished composite part; for aircraft primary structure.
- Oven cure occurs in two steps: first, cure under vacuum and then postcure in an oven at 350°F/180°C
Conventional process vs VaRTM
With the A-VaRTM process mechanichal properties similar to prepreg have been achieved.
The new process improves costs in all the aspects. Cost associated to materials are lower , the composite manufacturing using oven heating to cure is cheaper, we see cost improvements even in assembly and quality assurance. Although aluminium is still more cost competitive, A-VaRTM gets very close to it, as the component in composite has only 1.2 times the cost of the aluminium part.
The VaRTM uses dry fabric that is not impregnated with resin so the material is easier to fit around a three dimensional geometry.
The composite manufacturing cycle times have also been dramatically reduced on the stringers. They are cobonded with the precured skin panel, using a film adhesive, and the assembled component is subsequently postcured in an oven more than 19.7-ft/6m long.
Therefore Liquid Moulding with dry (engineered) fabrics proves succesful for the composite manufacturing of exigent aeronautic parts at lower overall costs.
You will find more information in the following articles : FightGlobal; CompositesWorld; MHI(1); MHI(2) ; ICCM